The invention concerns a holding apparatus for, in particular, a dental workpiece comprising a holding element and a fixing device. The workpiece can be fixed to the holding apparatus by a movement of the fixing device relative to the holding element. In addition, the invention concerns a set comprising such a holding apparatus and a dental workpiece. Furthermore, the invention also concerns a processing machine having such a holding apparatus. In addition, the invention concerns a process for the production of a holding apparatus and a processing machine for carrying out that process.
Various apparatuses such as CNC machines have been used for many years in dental laboratories for producing or processing dental workpieces in an automated procedure. An important aspect in that respect is that the dental workpiece which is usually in the form of a blank is securely held so that exact processing of the dental workpiece by way of a processing tool is possible. For that purpose, there are already various holding apparatuses which usually have a kind of holding element (also referred to as a holding frame or carrier plate) and a fixing device for the workpiece on the holding element.
An example of this can be seen from DE 100 37 531 A1, which discloses an apparatus for the production of dental workpieces. In that case, an opening for a blank is provided in a carrier body. The carrier body can be gripped in a processing machine with its outside. The blank is connected only to a part of the opening. A central rectangular opening serves to receive the cylindrical blank. The blank is glued at two opposite surfaces to the corresponding walls of the opening. That adhesive mounting is relatively complicated and expensive and leaves residues behind. In addition, an embodiment having an adhesive-free holding arrangement is shown, for example, involving a mechanical positively locking connection achieved by the blank itself having two mutually opposite mushroom-shaped projections which engage into an opening. A disadvantage with this variant is that the blank itself must have a relatively complicated configuration. In addition, the loading on the blanks in the region of the projections or in the enlarged region is relatively high. With this direct connection variant, damage to the blank cannot be excluded, in particular due to the high pressure loading.
A further holding arrangement for workpieces is disclosed in EP 2 026 931 B1. In accordance therewith, a clamping frame has an opening in which inwardly freely projecting support portions are provided on the clamping frame. A clamping device is also provided on the clamping frame. A frame-shaped holding arrangement can be secured to the clamping frame by that clamping device. Once again, the workpiece is glued or welded in that holding apparatus, and is preferably held in force-locking and/or positively locking relationship. It is stated generally that the workpiece together with the holding arrangement can be fitted fixedly and non-displaceably in a cutting machining apparatus by a clamping device, more specifically on a clamping frame which can be inserted therein. However, that specification does not explain how precisely the force-locking and/or positively locking connection between the workpiece and the holding arrangement is made.
US 2009/0274994 A1 discloses a dental milling machine based on a CNC machine. In this case, the individual blanks are fixed to the holding frame by a projection. The precise fixing mode is not described in greater detail, rather this involves being able to fit smaller or larger blanks.
DE 20 2010 001 125 U1 also shows an apparatus for holding and/or gripping blanks serving for the production of dental prostheses. For that purpose, an outer annular receiving device having a receiving opening is provided. The blank can be held in the receiving device directly by clamping means or clamping claws. It is, however, also possible for an adaptor to be fitted into the receiving device instead of a large blank, in which case in turn a blank or a plurality of blanks are mounted to the adaptor. The clamping claws are mounted releasably or interchangeably to the receiving device, and it is possible to use clamping claws of varying lengths to hold blanks of differing thicknesses. A disadvantage here is that the clamping claws bear directly against a relatively small region of the blank, whereby a relatively high pressure acts on the blank in that region. That can lead to unwanted deformation or overloading of the blank material.
In addition, WO 2013/117540 A1 shows a blank receiving means for a dental milling machine. Accordingly, there is an outer gripping holder and an inner workpiece holder on which in turn a support projection for the blank is provided. The arrangement further includes a clamping device which presses the blank against the support projection. The clamping device is releasably mounted by screw bolts to the workpiece holder. This, therefore, involves a clamping action for the blank between the clamping device and the support projection. Here, too, there is the disadvantage that direct clamping is effected in a small region of the blank and the blank must be of a relatively complicated shape. In addition, relatively many components are required for the fixing action.
DE 41 37 563 C1 discloses an apparatus for receiving workpieces of varying dimensions, and blanks of a differing external contour are gripped between prism carriers. Cam projections are provided for uniform opening at both sides, the projections engaging into semicircular recesses in a curved body. Due to the curved contour of the recesses, the displacement travel that the prism carriers cover is identical and in each case of the same magnitude, relative to the theoretical central axis. That, therefore, gives a curved narrowing of clamping surfaces. In this case, too, a relatively large number of components are required for the fixing action.
DE 10 2010 061 116 A1 also discloses a process for the production of dental workpieces, in which a workpiece is connected to a glued frame for fixing in a workpiece holder by a clamping action. In that case, the workpiece itself can be provided with a projecting step or with a notch into which a congruent counterpart portion of the clamping device engages in the region of an axis in the form of a wedge. That clamping or wedge action in this case is also detrimentally implemented directly at a relatively small region of the workpiece and can thus cause damage in the workpiece to be held.